Filler piece for double drum drier

ABSTRACT

A substantially prismatic filler piece having two concave arcuate side surfaces and located in the nip of a double-drum drier increases the rate of recovery of dry chlorosulfonated polyethylene from its solutions by about 10-40 percent. The filler piece should preferably occupy 40-60 volume percent of the nip. The radii of curvature of the side surfaces are the same as or larger than the radii of the drums.

United States Patent 1191 Peterson Sept. 24, 1974 FILLER PIECE FOR DOUBLE DRUM DRIER [75] Inventor: Henry Embry Peterson, Beaumont,

Tex.

[73] Assignee: E.I. du Pont de Nemours and Company, Wilmington, Del.

22 Filed: Dec. 19,1973

21 Appl. No.: 426,030

52 u.s.c1 34/17, 34/112, 34/113, 159/11 R, 165/91, 264/53, 425/224 1511 1111. c1. ..F26b 7/00 [58] Field of Search 34/10, 25, 108, 109, 110, 34/112-115, 17, 60; 165/91; 159/9, 10, 11 R, 12, 43 R, 49; 264/53; 425/224 [56] References Cited UNITED STATES PATENTS Kalil 264/53 3,068,585 12/1962 Overton 34/17 3,082,541 3/1963 Moore et a1. 3,115,433 12/1963 Eolkin et a1 159/11 R Primary Examiner-Kenneth W. Sprague Assistant Examiner-James C. Yeung [57] ABSTRACT A substantially prismatic filler piece having two concave arcuate side surfaces and located in the nip of a double-drum drier increases the rate of recovery of dry chlorosulfonated polyethylene from its solutions by about 104O percent. The filler piece should preferably occupy 40-60 volume percent of the nip. The radii of curvature of the side surfaces are the same as or larger than the radii of the drums.

7 Claims, 2 Drawing Figures FILLER PIECE FOR DOUBLE DRUM DRIER BACKGROUND OF THE INVENTION Chlorosulfonated polyethylene is well known in the art. It is ordinarily made by treating a dilute solution of polyethylene in carbon tetrachloride with chlorine and sulfur dioxide or with sulfuryl chloride, as taught, for example, in U.S. Pat. Nos. 2,586,363 and 3,299,014. The polymer may be isolated, for example, by evaporating the solvent on a drum drier andstripping the polymer film from the drier surface as a self-supporting reticulate film. This process is described in Pat. No. 2,923,979 (to Kalil). Drum driers, according to the Kalil patent, are steam heated to above lO-200C and may be arranged in pairs or as single drums. In a two-drum arrangement, chlorosulfonated polyethylene solution is introduced into the nip between the drums and is carried therefrom on the surfaces of the drums. The dry polymer film is removed from the drum surfaces with the aid of doctor knives.

In the drying of a polymer solution on a double-drum drier there are a number of variables which affect drying rate, and the relationships among them are complex. Some such variables, for example, are drier temperature, drum speed, nip setting (distance between surfaces of drums at closest approach), proportion of nip volume filled with polymer solution, polymer concentration in solution, and temperature at which solution is fed to the drier. For a given polymer solution and a given drier configuration there will exist an optimum set of drying conditions that will yield dry chlorosulfonated polyethylene at the maximum rate without causing degradation of the polymer by excessive exposure to heat.

SUMMARY OF THE INVENTION According to this invention, it now has been discovered that the production rate of a double-drum drier can be increased beyond that obtainable under the most favorable conditions for a given drier configuration by locating a substantially prismatic filler piece having concavearcuate sides within the nip between the drums. The filler piece is of approximately the same shape as the nip of the drier, and its size and location are such that it fills at least one-third and up to about three-quarters of the total nip volume. The filler pieces length is substantially equal to the width of the drum surface. The filler piece allows production rates to be increased by about -40%.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 represents a simplified view ofthe filler piece, together with its means of support.

FIG. 2 shows the filler piece in position within the nip of a double-drum drier.

DEFINITION For the purpose ofthe present invention, the nip vol- DETAILED DESCRIPTION OF THE INVENTION A representative form of equipment within the scope of this invention is illustrated in FIG. 1. The specific ume is the volume bounded by the following surfaces:

filler piece depicted in FIG. I is a prism having two arcuate surfaces, one of them being ABCD, each having a radius of curvature of r. Vertical distance from the point of contact of the two arcuate surfaces to the opposite surface is designated as h. The filler piece is suspended by way of attachment through vertical supporting members 2 and 3 from a horizontal member 6 which is provided with means for adjusting and'fixing the position of the filler piece within the nip of the drum drier. Means are provided for optionally heating the filler piece. For example, such means may comprise providing a hollow filler piece through which steam can be circulated. Nipples 4 and 5 are steam inlet and outlet, respectively, for providing such circulation.

Referring now to FIG. 2, the apparatus comprises two drier drums 7 and 8, each having radius r and rotated at equal peripheral speeds in opposite directions, as shown by the arrows. The drums are separated from each other by a small adjustable distance, forming a nip. These drums may be enclosed in a housing, not shown. An inlet pipe, 9, terminates above the nip of the drums. Knives 10 and 11 are placed about 45 from the tops of the drums and press against the surfaces of the drums to aid in separating the sheets of dried chlorosulfonated polyethylene from those surfaces. A current of air or an inert gas may be introduced through perforated pipes 12 and 13 to remove residual solvent and at the same time cool the polymer sheet 14.

The nip filler I of FIG. 1 is shown in FIG. 2 supported within the nip between the drums 7 and 8 by supporting means 2, 3, and 6.

In operation, the drums are steam-heated to the desired temperature and rotated as shown. A solution of chlorosulfonated polyethylene in carbon tetrachloride is delivered through the pipe 9 at such a rate that the nip is partly filled. The solution is carried onto the surfaces of the drums, where the solvent evaporates, and the polymer film is recovered.

As discussed in US. Pat. No. 2,923,979, the arrangement may be different in that the drums may rotatein directions opposite to those shown in FIG. 2, and the film of plastic then forms on upper, rather than lower, surfaces of the drums. The film is removed from the drums on its way down, rather than on its way up. The nip filler of the present invention is suitable for both drum drier designs.

The critical design features of a filler piece of the present invention include the degree of curvature of its sides, the proportion of the nip volume occupied by the filler, and the distance of closest approach of the surfaces of the filler piece to the surfaces of the drums.

The degree of curvature is bestexpressed in terms of the radius of curvature r. As r increases, the degree of curvature decreases and the sides of the prism become flatter. Depending then on the degree of curvature on the sides of the filler piece, the filler piece may be in closely spaced relationship with the drums over substantially total area of its sides, or it may be close to the drums at only one point. It is important that the filler piece be close to the drums in its lower portion, that is, along the AD edge of the piece in FIG. 1, as that edge approaches the horizontal center line of the drums. The clearances between the lowest edge of the prism and the drum surfaces should be about 1/8 to 3/16 inch on each side. The radius of curvature 2'' should be at least equal to that of the drums, r, and the centers of curvature of these surfaces preferably should be separated by a distance of two radii, that is 2r. Placing the centers substantially closer than 2r or having surfaces with radii r substantially less than the drum radii r would result in the undesirable situation where the clearance between the filler piece and the drums would decrease from the deepest point outward. The clearances should increase from the bottom to the top.

The volume of the nip occupied by the filler piece preferably should be between about 40 and 60 percent. Ordinarily the filler piece would be placed as far down in the nip as possible. The filler piece volume is varied by varying the height h of the filler piece, shown in FIG. 1.

The nip filler piece should be made of a material resistant to corrosion, heat, and chlorinated hydrocarbon solvents. Titanium is the preferred construction material for a filler piece of the present invention. For 501- vents other than chlorinated hydrocarbons other construction materials may be found to be equally suitable yet less costly.

The filler piece can be either solid or hollow inside, but it preferably should not be open to the polymer solution because such open piece would be difficult to empty and also could cause contamination problems. The top surface of the filler piece has been represented in FIGS. 1 and 2 as a straight, horizontal surface. However, it is not required that the top surface of the device be horizontal. It may be, for example, slanted, arcuate, or irregular in shape and still will not impair the performance of the filler piece.

The following example illustrates the invention and provides comparative production rate data for a double-drum drier with and without a filler piece.

EXAMPLE The apparatus in FIGS. 1 and 2 of the drawings was employed to isolate chlorosulfonated polyethylene which contained 35 percent chlorine and 1 percent sulfur from a solution in carbon tetrachloride in which the concentration of chlorosulfonated polyethylene was about 13 percent by weight. The ratio of the length to the diameter, 2r, of the drums of the dryer was 2.4. A filler piece was used which had two arcuate surfaces having radii of curvatures, r in FIG. 1, both equal to the radius of the drums of the dryer, 1 in FIG. 2, the centers of curvature being separated by a distance of two radii. The height of the filler piece was equal to about 0.94 radius. The filler piece was positioned within the nip so that a clearance between the deepest tip and thesurface of each drum was 3/l6". In this position the filler occupied about 49 percent of the volume of the nip. The filler piece was not heated in this example. Solution of the chlorosulfonated polyethylene was fed into the nip of the dryer at a rate sufficient to maintain the level of fluid in the nip at the top of the drums, The drums were internally heated with steam at psi and rotated at 8 rpm. Drum surfaces were thereby coated with chlorosulfonated polyethylene which after separation as a dry film from the hot drum contained less than 0.25 percent by weight of carbon tetrachloride.

When the run was repeated without the filler piece, it was necessary to reduce the production rate to about 82.4 percent of the output of the first run in pounds per hour per square foot of drum surface area, to isolate a dry film having a carbon tetrachloride content of not over 0.25 percent by weight. Alternatively, based on the production rate without the filler piece, the production rate according to the process of the present invention, with the filler piece in place, was 2l percent higher.

I claim:

1. In a process for recovering dry chlorosulfonated polyethylene from its solutions by drying said solutions on a double-drum drier, the improvement of placing in the nip of the drier a substantially prismatic filler piece having concave arcuate sides; its length being substantially equal to the width of the drum surfaces, and the radii of curvature of its sides being at least equal to the radii of the drums; said filler piece occupying at least one-third and up to about three quarters of the total nip volume.

2. The improvement of claim 1 wherein the filler piece occupies about 40-60% of the nip volume.

3. In a double-drum drier used for the evaporation of chlorosulfonated polyethylene, a substantially prismatic filler piece having concave arcuatc sides; its length being substantially equal to the width of the drum surfaces, and the radii of curvature of its sides being at least equal to the radii of the drums; said filler piece occupying at least one-third and up to about three-quarters of the total nip volume.

4. The filler piece of claim 3 occupying 40-60% of the nip volume.

5. The filler piece of claim 3 being so placed that the clearance between its lowest edge and the drum surfaces is about As to 3/16 inch on each side.

6. The filler piece of claim 3 made of titanium.

7. The filler piece of claim 3, the radii of curvature of its concave sides being substantially equal to the radii of the drums, and the centers of curvature being separated by substantially the length of two radii. 

2. The improvement of claim 1 wherein the filler piece occupies about 40-60% of the nip volume.
 3. In a double-drum drier used for the evaporation of chlorosulfonated polyethylene, a substantially prismatic filler piece having concave arcuate sides; its length being substantially equal to the width of the drum surfaces, and the radii of curvature of its sides being at least equal to the radii of the drums; said filler piece occupying at least one-third and up to about three-quarters of the total nip volume.
 4. The filler piece of claim 3 occupying 40-60% of the nip volume.
 5. The filler piece of claim 3 being so placed that the clearance between its lowest edge and the drum surfaces is about 1/8 to 3/16 inch on each side.
 6. The filler piece of claim 3 made of titanium.
 7. The filler piece of claim 3, the radii of curvature of its concave sides being substantially equal to the radii of the drums, and the centers of curvature being separated by substantially the length of two radii. 